The present invention relates in general to terminals for optical fibers and, in particular, to an over-molded terminal with an integral reflector for non-axial signal communication applications. The invention has particular advantages for certain photoplethysmography applications.
Optical fibers are used to transmit optical signals in a variety of applications including communications, spot or area illumination and photoplethysmography, e.g., pulse oximetry. The associated optical systems typically include one or more fiber terminals where signals are transmitted to and/or from an end of an optical fiber. In this regard, such terminals are often associated with optics such as lenses or mirrors, for example, for focusing an incoming signal onto the fiber end, for forming an outgoing signal into a beam, for diffusing an outgoing signal as may be desired or for various other functions. One important function of such optics is to receive or transmit non-axial signals, i.e., signals not aligned with the optical axis extending from the fiber end. It may be desired to transmit or receive non-axial signals, for example, in order to reduce optical system dimensions, to couple the optical fiber with other optical components that are constrained to being located off-axis, or to facilitate selective coupling of the fiber relative to multiple optical devices which cannot all be disposed on-axis.
Accordingly, it is often desired to provide a reflector or mirror in connection with a fiber terminal. Depending on the intended use of the mirror, many different optical, construction and maintenance issues may need to be considered in connection with the terminal/mirror interface. One of these issues relates to the relative positioning of the fiber end and the mirror. The fiber end generally must be securely anchored and the mirror must be carefully positioned on the fiber axis in order to allow for proper optical coupling of the mirror to the optical fiber. The angular orientation of the mirror generally must also be controlled in relation to the overall optical system for proper alignment so as to reduce optical losses. Additionally, the distance between the fiber end and the mirror may need to be selected in conjunction with the mirror shape such that incoming signals are focused or contrasted on the fiber end, or outgoing signals from the fiber end are focused, collimated or diffused as desired, etc. Moreover, for maintenance purposes, the mirror may need to be sealed or be accessible for cleaning in order to maintain acceptable optical performance. It will thus be appreciated that the design, construction and maintenance of fiber terminals and associated optics can be complicated and expensive.
The present invention is directed to an integrated fiber terminal and reflector system for use in a variety of off-axis signal transmission applications including transmitting and/or receiving signals that are off-axis relative to a terminated fiber. The invention substantially simplifies construction, alignment and maintenance, and allows for reduced production costs as well as improved optical performance. As set forth below, the invention has particular advantages for certain photoplethysmography applications such as pulse oximetry due to its compactness of design, ease of construction and alignment, and low production costs for probes that may be disposed of after a single use or few uses.
According to one aspect of the present invention, a reflective surface is integrally formed on a signal transmissive terminal structure in which a fiber is anchored. The corresponding terminal includes a terminal structure for fixedly retaining an end portion of the optical fiber such that the fiber end portion defines a fiber axis extending axially from the end portion, and a reflective surface integrally formed on the terminal structure and extending across the fiber axis. The terminal structure includes an optically transmissive portion extending across the fiber axis. Preferably, the optically transmissive material is substantially transparent to at least one wavelength of interest. For example, the terminal structure or a portion thereof may be formed from transparent plastic that is molded over the end portion of the fiber. The reflective surface is operative for reflecting signals relative to the fiber axis and a reflection axis, i.e., reflecting signals from the fiber axis to the reflection axis or vice versa. Preferably, the reflective surface is integrally formed on the terminal structure by applying a reflective film or other reflective material to an external surface of the terminal structure. In this regard, the exterior surface of the terminal structure may be shaped to impart the desired optical properties to the reflective surface, e.g., concentrating/focusing, collimating, or diffusing optical signals incident thereon. By virtue of the present invention, construction and alignment of the terminal/mirror system is simplified and costs are reduced. In addition, the reflective surface may be protected against dust or other optical interference. Moreover, a compact and reliable terminal system for off-axis applications is provided.
If desired, a further optical device may be mounted on the terminal structure. For example, the optical device may be mounted on an exterior surface of the terminal structure extending across the reflection axis in order to operate on signals transmitted along the reflection axis, e.g., incoming or outgoing signals. Depending on the application, the optical device may perform any of various functions. For example, the optical device may diffuse signals transmitted from the optical fiber in order to illuminate a desired area. Alternatively, the optical device may collimate, concentrate or focus signals transmitted from the optical fiber onto a further optical element such as another optical fiber, a lens, or an optical detector. Conversely, the optical device may operate on incoming signals, for example, to focus or assist in focusing the incoming signal onto the end of the terminated optical fiber.
According to another aspect of the present invention, a method is provided for forming an optical fiber terminal. The method includes the steps of providing an optical fiber having an exterior buffer material, removing the buffer material from an end portion of the fiber, molding an optically transmissive material over the end portion of the fiber, and applying a reflective material to an exterior surface of the molded, optically transmissive material such that the reflective material extends across an axis of the fiber. The buffer material may be a liner material such as is commonly provided in connection with optical fibers to prevent accidental breakage or shield ambient light. Such buffer material can be removed from the end portion by way of a conventional stripping operation. The optically transmissive material may then be molded over the end portion of the fiber, for example, by way of injection molding transparent plastic on the optical fiber end. As part of this molding process, and exterior surface of the plastic may be shaped to impart desired optical properties to the reflective material subsequently applied to the exterior surface. Depending on the nature of the optically transmissive material and the reflective material, the reflective material may be applied by direct deposition onto the optically transmissive material adhesive bonding, or other processes. In the case of adhesive bonding, the adhesive may be applied outside of the area of the reflective surface or an index matched adhesive may be employed. In all such cases, it is an advantage of the present invention that the reflective material is integrally formed on the terminal structure such that proper optical performance is insured.
In one embodiment, the optical terminal of the present invention is implemented in connection with a pulse oximeter probe. Pulse oximetry generally involves transmission of optical signals of a predetermined wavelength or wavelengths through a portion of a patient""s body such as a finger, ear lobe or the like. The optical signal transmitted through the patient""s tissue is then detected and can be analyzed to determine oxygen saturation, perfusion or the like as is well known. It is desirable to provide the portion of the oximeter instrument which engages the patient in the form of a detachable probe. Such a probe may be disposed of after a single use or a small number of uses. Accordingly, it is desirable to reduce the cost of the probe by locating relatively few components in the probe but, rather, locating most of the active and expensive components in an oximeter housing to which the probe is coupled. Thus, for example, the use of fiber optics can allow a signal source and/or a signal detector to be located in the housing.
Accordingly, the probe may include a transmitting fiber and associated optics and/or receiving fiber and associated optics. Alternatively, the receiving fiber and associated optics may be replaced by a detector and electrical leads. The probe also includes a housing structure for engaging the patient. For example, the housing may be shaped and dimensioned for engaging a patient""s finger. In accordance with the present invention, the terminal of the present invention may be engaged within the probe housing structure for transmitting and/or receiving pulse oximetry signals. In this regard, the terminal structure may be bonded to the probe housing structure or may be removably inserted into the housing structure with appropriate mechanisms to insure proper registration of the transmitting and receiving elements.